Circuit interrupter apparatus



CAL

Patented Mar. 18, 1941 UNITED STATES PATENT OFFICE CIRCUIT INTERRUPTER APPARATUS vania Application September 15, 1939, Serial No. 295,098

8 Claims.

My invention relates to circuit interrupting systems, and has particular relation to apparatus in which the arc is extinguished in a liquid, such as oil, when a circuit breaker is opened.

In circuit interrupters constructed in accordance with the teachings of the prior art, the arc ignited between the contacts, when they are opened, is moved rapidly through the liquid; As a result of the motion vigorous turbulence is created and the ionization which tends to maintain the arc is suppressed. Circuit interrupters depending on turbulence for deionization have operated satisfactorily for voltages of moderate magnitude. I have found, however, that for relatively high potentials of the order of several hundred kilovolts, considerable time is required to completely extinguish the arc, and at times, the breaker fails entirely because the arc continues for an excessive interval. In a circuit breaker for 287 kilovolts, ten three-inch breaks were found to be necessary.

It is, accordingly, an object of my invention to provide an arc-extinguishing device for a circuit breaker designed to interrupt a relatively high potential.

Another object of my invention is to provide a device for quickly extinguishing the arc which is ignited when a circuit breaker designed to interrupt a high potential. of the order of several hundred kilovolts is opened.

More specically stated, it is an object of my invention to provide in a circuit breaker having a high voltage rating for an alternating current system, a contrivance by the operation of which the arc shall be completely extinguished within an interval of time corresponding to one cycle of alternating current at a frequency of the impressed voltage on the system in which the breaker is connected.

My invention arises from the realization that there is a limit to the voltage which can be handled in the prior art apparatus after arc extinction because the gases generated by the arc are not removed from the potential field. As the arc moves through the liquid in the prior art apparatus, it leaves behind it a series of bubbles. At current zero the volume of the arc enclosing bubble is greatly reduced compared to the bubble which would exist if there were no arc motion. The interrupting ability of the breaker depends on the reduction in the section of the bubble which thus takes place. The bubbles contain gas which is of much lower dielectric strength than the oil and because they remain between the contacts oi the breaker an arc is reignited in the (Cl. 20D-150) bubbles with return of the high voltage after the original arc has been extinguished.

My invention contemplates the removal of the bubbles which the arc leaves behind it from the field between the electrodes. In accordance with my invention, the arc is rotated in a closed curve, such as a circle, and is at the same time confined between insulating baffles which permit the liquid to circulate freely. The rotation is produced by a magnetic eld which is of sufficient magnitude to produce a high velocity. In general, I have found that for the interrupters with which I am primarily concerned, the eld may have a magnitude in gausses equal to one-half the arc-current in amperes. In one case to which my invention is applicable the arc-current flow is of the order of 8000 amperes. The motion of the arc imparts a rotational velocity to the liquid andthe ionized bubbles are removed from the region between the electrodes and projected into the region between the baiiles by the circulation of the liquid which results from the centrifugal force in the'liquid.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawing, in which:

Figure 1 is a view partly in section, showing a. circuit breaker in accordance with my invention;

Fig. 2 is an enlarged view in perspective showing the formation of bubbles between the contacts of a circuit breaker when the are is moved; and

Fig. 3 is an enlarged view in perspective showing the removal of the bubbles formed between the contacts in accordance with my invention.

The apparatus shown in Figure 1 comprises a tank 5 of the usual structure containing an insulating liquid, such as a suitable oil, for example. A pair o! threaded terminal rods 'l extend through insulating bushings 9 which project into the tank through the top Ii. Shields i3 of an insulating material such as porcelain cover the bushings 9 and are supported by discs i5 which are screwed on the rods 1 and abut against washers I1.

The xed contacts I9 of the circuit interrupter are supported from brackets 2|, each of which consists of a disc-shaped portion 23 having a central threaded boss 25 extending at an oblique angle to the disc. The terminal rods 1 are screwed into the bosses 25 and the fixed contacts l I9 are thus suspended from the rods. An assembly consisting of a cylindrical insulator 21 and a stack of annular insulating bailles 29 of substantially the same outer diameter as the disc 23 and the insulator 21 abuts the face of the disc opposite' to the boss 25. The baffles 29 are held apart by spacers 3| and abut the lower side of the insulator.21. The insulator and baille assembly is held together by insulating bolts 35 which extend through the bailies, the spacers and the insulator and engage threaded openings on the ring of the disc portion 23 of the bracket 2 I. The spacers 3| are of small diameter and have a thickness to provide suiiicient space between the bailies 29 to permit the liquid to freely move therebetween. The insulators 21 have an annular recess extendingupwardly from the lower side thereof to form a central projection 31 and an outer rim portion 33.

The xed contacts I9 are of ring cross-section and are secured to the central projections 31 of the insulator 21. A coil 39 which provides a magnetic field for rotating the arc is disposed in the recess between the rim 33 and the central projection 31 of each of the insulators 21 and is supported on the baille 29 which abuts the insulator. 'I'he upper terminal 4| of each coil 39 is connected to the lower i'ace of the corresponding bracket 2| and the lower terminal 43 is connected to the corresponding fixed contact I9. The coils 39 are thus in circuit with the terminal rods 1 and the fixed contacts |9.

'I'he movable contacts 45 are also of ring crosssection and are mounted near the ends of a conducting cross bar 41. A slidable lif-t rod 49 is secured at the center of the bar 41 and the rod is moved up and down to engage and disengage the contacts |'9 and 45. The mechanism y for moving the rod may be any device well known in the art, and as. it does not concern the invention, itis not shown.

When the contacts I9 and 45 are closed, current ows in a path extending through one of the terminal rods 1, through the corresponding coil 39, the corresponding contacts |9 and 45, the cross bar 47, the contacts associated with the other -terminal and the other coil 39 to lthe other terminal. No diiliculty is involved from the fact that the coils 39 are in circuit with the contacts is and 45 as the coil impedance is small.

When the cont'cts are opened, arcs are ignited between each fixed contact i 9 and the associated movable contact 45. Under the action of the magnetic field produced by the coils 39, the arc is moved rapidly around the erstwhile engaging surfaces of the contacts. As it moves, it leaves behind it a series of bubbles. The structure and formation of the bubbles can be seen from Fig. 2. When the arc is rst ignited between the contacts the heat vaporizes the oil enclosing i. and a bubble 5| enclosing the arc is formed. As the arc moves around the contacts i9 and 45 it leaves behind it a mass of smaller bubbles 52. As the current iiow through the arc decreases, the volume of the arc-enclosing bubbles decreases until a thin column of gas, as represented by the line 53 in Fig. 2, remains. The original arc disappears in the region of this bubble 53. However, if the mass of small bubbles 52 remain between the electrodes, they provide a space of low dielectric strength in which the arc is reignited when the potential rises from the zero value.

i In accordance with my invention, the reigni-tion prevented by the removal of the bubbles. The

rotation ofthe arc produces substantial motion in the' liquid and under the centrifugal force the liquid moves outwardly and carries with it'the bubbles 52 as shown in Fig. 3. The bubbles are further broken up by .the insulating bailles 29 5 and there is no ionized region in which the arc may be reignited.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. A circuit interrupter comprising a liquid medium, cooperative contacts to be engaged and disengaged and having engaging surfaces permitting the point-to-point movement of an arc ignited between them immersed in said medium, means for restricting the arc to the region of said contacts but permitting the free circulation of said liquid, and means for moving an arc, after it has been ignited, over said engaging surfaces at a speed such that the forcearising from the 25 resultant motion of the medium in a direction transverse to the arc ejects the bubbles left by the arc as it moves from the vicinity of said coni tacts and said restricting means.

2. A circuit interrupter comprising a liquid 30 medium, cooperative contacts -to be engaged and disengaged and having engaging surfaces permitting the point-to-point movement of'an arc ignited between them immersed in said medium, a plurality of insulating baiiies disposed 'to restrict the arc to the region of said contacts but permitting the tree circulation of said liquid, and means for moving an arc, after it has been ignited, over said engaging surfaces at a speed such that the force arising from the resultant motion oi the medium in a direction transverse to the arc elects the bubbles left by the arc as it moves from the vicinity of said contacts and into the region between said baiiles.

3. A circuit interrupter comprising a liquid medium, cooperative contacts to be engaged and disengaged and having curvilinear engaging surfaces permitting the point-to-point movement of an arc ignited between them, means for restrieting the arc to the region of said contacts, and means for moving an arc after it has been ignited, over saidisurfaces at a speed such that the centrifugal force arising from the resultant motion of said liquid in a direction transverse to said arc ejects the bubbles left by the arc as it moves from the vicinity of said contacts and beyond said restricting means.

4. A circuit interrupter comprising a liquid medium, cooperative contacts to be engaged and disengaged and having curvilinear engaging surfaces permitting the point-to-point movement of an arc ignited between them, a plurality of insulating baffles disposed to restrict the arc to the region of said contacts, and means for moving an arc after it has been ignited, over said surfaces at a speed such that the centrifugal force arising froni the resultant motion of said liquid in a direction transverse to said arc ejects the bubbles left by the arc, as it moves, from the vicinity of said contacts and into the region between said bailles.

5. A circuit interrupter comprising a liquid medium, cooperative contacts to be engaged and disengaged and having engaging surfaces permitting the point-to-point'movement of an arc 75 ignited between them immersed in said medium, means for restricting the s' to the region of said contacts, said restricting means being permeable to the iiuid from the region 0f said arc, and means for moving an are, after it has been ignited, over said engaging surfaces at a speed such that the uforce arising from the resultant motion of the medium in a direction transverse to the arc ejects the bubbles left by the arc as it moves from the vicinity of said contacts and said restricting meals.

6. In a circuit interrupter, a. quantity of are extinguishing liquid, are terminal members im mersed in said liquid, said arc terminal members being spaced from each other at least during the circuit interrupting operation and being arranged to provide generally annular are termiu nal paths thereon, means for establishing an arc between said arc terminal members, means for moving said arc laterally along said arc terminal paths at a speed such that liquid is caused te iiow in a direction transverse to said arc, and ior restricting said arc to the region beu tween said arc terminal members, said arc restrcting means being pervious to the dow of liquid and are gases to enable said moving liquid to sweep the arc gases from the region between said arc terminal members.

'1. in a circuit interrupter, a quantity of are extinguishing liquid, arc terminal members lmmersed in said liquid, said arc terminal members being spaced from each other at least during the circuit interrupting operation and being arranged to provide generally annular arc terminel paths thereon, means for establishing an arc between said arc terminal members, baffle members disposed to conne the arc to the space between said arc terminal members, and means for moving the arc laterallg,T along said arc terminal paths at a speed such that a quantity of said liquid is caused to be moved outwardly through said baiiie members, said baille mem* bers being so arranged to permit the free now cf liquid therebetween to enable saidmoving liquid to carry the arc gases from the space be tween said arc terminal members.

8. Ln a circuit interrupter, a quantity of arc extinguishing liquid, a pair of are terminal members immersed in said liquid and being adapted te be separated from each ether at least during the circuit interrupting operation, said arc ter-7 minal members having annular arc paths theren on between which an arc is adapted to play, means or establishing ari arc between said are terminal members, a plurality oi insulating bar rier plates oi annular form disposed spaced relation with respect to each other about said arc terminal members so as to restrict the outward movement of said arc beyond said an nular are paths, and means for spinning said are laterally around said annular arc paths at a rate suicient to cause a radial dow o liquid away from the space between said arc terminal members and through the spaces between said barrier plates, said iiow of liquid being sullcient to sweep the arc gases from the space between said arc terminal paths and discharge said gases through the spaces between said barrier plates..

JOSEPH SLEPIAN. 

